The present invention generally relates to electric distribution and specifically to convenience outlets having a new and improved safety receptacle, i.e. a contact system installed at an outlet of electricity for connection of at least one attachment plug having at least two contact pins and being of the general type used for supply of electricity, e.g. at 110 or 220 Volts, to portable equipment, such as lamps, appliances, electronic equipment, tools, machines, instruments, etc., at currents of typically up to 10 Amperes.
As is well known, conventional receptacles including wall sockets and flush sockets represent a constant source of danger, notably in a household with children, and the art is replete with suggestions of safety devices or safety receptacles.
The general definition of a safety receptacle is that it is made to prevent an unintended or accidental contact of the human body, e.g. the hand of a playing child, with any live parts of the socket. Substantially all types of receptacles or sockets include a lid or cover housing that conceals the live or potentially live parts which are accessible to the pins of a plug through openings of the front plate which is part of the cover housing or of the lid; while the openings have diameters of generally less than 5 mm and are too small to permit penetration by a child's finger, there is always the danger that the child may hold a small metal piece, e.g. a nail or needle, and tries to explore a socket in this manner. Further, when a plug is pulled from a socket by a child or a careless adult there is some danger that the hand which holds the plug while pulling will accidentally touch a part of a contact pin while the latter is still in contact with a live connector end of the receptacle or socket.
In essence, there are two groups of safety receptacles that aim at preventing such unintended body contact with live parts of the receptacle and/or a plug: the first group includes an entirely mechanical (that is, no switching of currents being involved) safety device in the form of a movable safety plate arranged behind the front plate, i.e. within the receptacle and resiliently held, e.g. by a spring, in a monostable "closing" position in which it intersects with the (theoretical) lines of pin movement between the perforations of the front plate and the connector ends. The safety plate or bar either has a wedged cross-section, or is provided with a bevelled edge or taper, and is moveably supported such that it will move out of intersection with the lines of pin movement only upon simultaneous introduction of the contact pins of the plug. Such movement of the safety plate or bar from its stable first or closing position into an "instable", i.e. self-reverting second or access-permitting open position, is generally perpendicular to the line (or lines) of pin movement and the safety plate will return by the action of its spring loading as soon as the plug is withdrawn.
In another group of safety devices a moveable plate or bar of the type just discussed is combined with an electrical safety device incorporating the basic features of a relay, i.e. an electric device designed to interpret certain input conditions in a predetermined manner and to respond to predetermined conditions by causing an abrupt electric change, e.g. making or breaking an electric circuit.
In prior art safety receptacles the relay responds to a switch that is operated by the moveable safety plate or bar and switches the energizing current of the relay which, in turn, connects the electric supply line with at least one connector end of the receptacle.
A main disadvantage of the simple or purely mechanical safety receptacles is that the safety plate or bar must be moveable across substantially the entire contact diameter of the connector ends; in practice this amounts to a displacement length of at least about 5 mm taking into account the normal configuration of the pin-receiving portion of the contact ends with their outwardly curved prong ends. Displacement of the safety plate along a path of such length in response to the pressure of the plug pins acting upon the safety plate at an angle of about 90.degree. will be felt as a substantial hindrance to normal plug insertion. The user will be caused or tempted to use excessive force when pushing a plug into such a receptacle and this may easily lead to damages of the receptacle which, in general, is a low-cost mass produced item.
Receptacles that include an electric safety device share this defect to some extent at least. While the safety plate of such receptacles need not cover the entire cross-section of the pin contacting portion of the connector ends, the required length of displacement must still be large enough to actuate the switch for the operating circuit of the relay; the space requirements of the relay switch and the relay proper constitute another disadvantage of such receptacles that tend to be more bulky than normal receptacles and require a larger volume of space for mounting.